Under the condition of current production process, Organic Light emitting Diode (OLED) display device has a temporal and spatial non-uniform issue. As the size of the display device is becoming larger, such issue is exposed even more seriously. Therefore, solving the display non-uniform issue in OLED display device of large size becomes one of the indispensable key techniques for mass production. The display non-uniform issue in OLED display device is closely related to the production process. The overall luminance uniformity of the display device goes worse when there is a relative large difference among threshold voltage values of the whole panel; and meanwhile, the organic material used for the display device also faces a problem that the luminance is changed constantly during the lifetime thereof. Therefore, said issues can not be completely solved through only improvement on the process and can only be solved by adopting various compensative driving.
There are two types of compensation methods, i.e., internal compensation and external compensation. The internal compensation method refers to a method of performing compensation by using sub-circuit constructed from Thin Film Transistor (TFT) inside the pixel. The external compensation method refers to a method of drawing the TFT or OLED signal external to backboard and performing compensation by an external Application Specific Integrated Circuit (ASIC). The pixel structure and the driving manner of the internal compensation are usually complicated and the compensation effect is limited to TFT threshold voltage and line voltage drop, and the residual image issue can not be solved. Meanwhile, in the display application of large size, high resolution and high refresh frequency, the internal compensation manner results in a reduced opening ratio and a slow driving speed. The external compensation method has advantages of having a simple pixel structure, a fast driving speed and a good compensation effect, and thus is considered as an optional compensation solution in the display of Active Matrix Organic Light Emitting Diode (AMOLED) of large size.
The external compensation can further be classified into optical drawing compensation and electrical drawing compensation depending on the drawing manner. The optical drawing compensation refers to drawing out a luminance signal through optical Charge Coupled Device (CCD) photographic method after lighting the backboard, and the electrical drawing compensation refers to drawing out electrical signals of TFT and OLED through a sensing circuit of a driving chip. The signals drawn in the two drawing method are of different kinds and data processes performed on them are also different. The optical drawing manner has advantages of having a simple structure and being flexible, and thus is widely used currently.